Process for preparing ethylenediphosphonic acids

ABSTRACT

The invention relates to a process for preparing ethylenediphosphonic acids of the formula I,  
                 
 
     where R 1  and R 2  may be identical or different and are hydrogen, a carboxy group, a carboxylic acid derivative, an unsubstituted or substituted alkyl group having from 1 to 10 carbon atoms, phenyl, benzyl, or alkyl-substituted aromatic systems, which comprises reacting phosphorous acid (H 3 PO 3 ) directly with alkynes.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a process for preparingethylenediphosphonic acids of the formula I,

[0002] where R₁ and R₂ may be identical or different and are hydrogen, acarboxy group, a carboxylic acid derivative, an unsubstituted orsubstituted alkyl group having from 1 to 10 carbon atoms, phenyl,benzyl, or alkyl-substituted aromatic systems.

[0003] Phosphonic acids are of great industrial importance, and theacids or their salts and esters are widely used in a very extensivevariety of application sectors. Examples of applications of phosphonicacids are water softening, ore floatation, heavy metal complexing, andtheir use as starting materials for preparing flame retardants,pharmaceutical products, and pesticides.

[0004] The many types of application using phosphonic acids to formsalts or complexes mainly use di- and polyphosphonic acids.Ethylenediphosphonic acids of the formula (I)

[0005] are particularly important here.

[0006] The known prior art uses complicated multistage syntheses toprepare ethylenediphosphonic acid (where R₁ and R₂ in formula I arehydrogen).

[0007] For example, K. Moedritzer, R. R. Irani, J. Inorg. Nucl. Chem. 22(1961) 297-304 describes by way of example a process which begins byreacting diethyl β-chloroethylphosphonate with potassium diethylphosphonate to give tetraethyl ethylenediphosponate, which is thenconverted into the desired ethylenediphosphonic acid by hydrolysis withconcentrated hydrochloric acid.

[0008] DE 21 58 765 A1 proposes a process which begins by reactingtriphenyl phosphite with tris(chloroethyl)phosphite with elimination ofdichloroethane to give tetraphenyl ethylenediphosphonate, which is thenconverted into the desired ethylenediphosphonic acid under acidic oralkaline conditions, with cleavage of phenol.

[0009] The process described in S. M. Shner, L. P. Bocharova, I. K.Rubtsova, J. Gen. Chem. USSR 37 (1967 390-392) also starts fromtris(chloroethyl) phosphite, which is reacted with ethyne(acetylene) togive tetrakis(chloroethyl) ethylenediphosphonate, which is thenconverted into the desired ethylenediphosphonic acid by hydrolysis underacidic conditions.

[0010] Disadvantages common to all of the above processes are that thestarting materials themselves require complicated and expensivepreparation, the yields obtained are inadequate, and considerableamounts of undesirable byproducts are produced, for example alkylhalides and phenols. This makes the processes uneconomic andenvironmentally unsatisfactory, so that ethylenediphosphonic acidsprepared by these processes are almost impossible to obtain andtherefore are not available for use in many possible applications.

[0011] There is therefore a requirement for a process which preparesethylenediphosphonic acids and is simple to carry out, and gives a highyield of pure products. This process should also be markedly superior ineconomic and environmental terms to those previously known, by usingreadily obtainable or readily synthesizable starting materials andproducing no undesirable byproducts.

SUMMARY OF THE INVENTION

[0012] The object on which the invention is based is therefore toprovide a process whch prepares ethylenediphosphonic acids and avoidsthe abovementioned disadvantages, and gives the desired product in asingle stage, starting from simple and readily obtainable materials.

[0013] This object is achieved by way of a process of the type mentionedat the outset, which comprises reacting phosphorous acid (H₃PO₃)directly with alkynes.

DETAILED DESCRIPTION OF THE INVENTION

[0014] The process of the invention has high selectivity and gives thecorresponding ethylenediphosphonic acids in very good yields. This isparticularly surprising since the experiments described in C. E.Griffin, H. J. Wells, J. Org. Chem. 24 (1959) 2049 give only low yieldsand considerable extent of side reactions on reacting phosphorous acidwith olefins.

[0015] Compared with the processes previously known, the process of theinvention has considerable advantages since it is single-stage, requiresno use of complicated or halogen-containing starting materials, produceshardly any byproducts, and is overall an extremely economic process.

[0016] The phosphorous acid is preferably reacted with alkynes in thepresence of a free-radical initiator.

[0017] The free-radical initiators used preferably comprise azocompounds.

[0018] The azo compounds are preferably cationic and/or noncationic azocompounds.

[0019] The cationic azo compounds used preferably comprise2,2′-azobis(2-amidinopropane) dihydrochloride or2,2′-azobis(N,N′-dimethyleneisobutyramidine) dihydrochloride.

[0020] The noncationic azo compounds used preferably compriseazobis(isobutyronitrile), 4,4′-azobis(4-cyanopentanoic acid), or2,2′-azobis (2-methylbutyronitrile).

[0021] The free-radical initiators used preferably comprise peroxidicinorganic and/or peroxidic organic free-radical initiators.

[0022] The peroxidic inorganic free-radical initiators used preferablycomprise hydrogen peroxide, ammonium peroxodisulfate, and/or potassiumperoxodisulfate.

[0023] The peroxidic organic free-radical initiators used preferablycomprise dibenzoyl peroxide, di-tert-butyl peroxide, and/or peraceticacid.

[0024] A wide selection of suitable free-radical initiators can be foundby way of example in Houben-Weyl, Supplementary volume 20, in thechapter “Polymerisation durch radikalische Initiierung”[Free-radical-initiated polymerization] on pages 15-74.

[0025] The free-radical initiators are preferably metered incontinuously during the reaction.

[0026] The free-radical initiators metered in continuously during thereaction are preferably in the form of a solution in the alkyne.

[0027] The free-radical initiators metered in continuously during thereaction are preferably in the form of a solution in the solvent used.

[0028] To prepare the ethylenediphosphonic acids, phosphorous acid isreacted in the presence of a free-radical initiator with alkynes of theformula (II)

R₁—C≡C—R₂  (II)

[0029] where R₁ and R₂ are identical or different and are hydrogen, acarboxy group, a carboxylic acid derivative, an unsubstituted orsubstituted alkyl group having from 1 to 10 carbon atoms, phenyl,benzyl, or alkyl-substituted aromatic systems.

[0030] The alkynes used may be either the unsubstitutedethyne(acetylene) where R₁ and R₂=H in formula (II), singly substitutedderivatives where R₁=H and R₂≠H in formula (II), or else doublysubstituted alkynes where R₁ and R₂ ≠H in formula (II).

[0031] Examples of these alkynes are ethyne(acetylene), phenylacetylene,diphenylacetylene, propyne, 1-butyne, 2-butyne, 1-phenylbutyne,1-pentyne, 2-pentyne, 1-phenyl-1-pentyne, 1-hexyne, 2-hexyne, 3-hexyne,1-phenyl-1-hexyne, 1-heptyne, 1-octyne, 4-octyne, 1-nonyne, 1-decyne,1-dodecyne, the alkynols propargyl alcohol, 1-butyn-3-ol, 2-butyn-1-ol,2-butyne-1,4-diol, 1-pentyn-3-ol, 2-pentyn-1-ol, 4-pentyn-1-ol,4-pentyn-2-ol, 3-hexyn-1-ol, 5-hexyn-1-ol, 3-hexyne-2,5-diol,2-octyn-1-ol, 1-octyn-3-ol, 3-nonyn-1-ol, 3-decyn-1-ol, and alsopropargyl chloride, propargyl bromide, propargylamine, propiolic acid,methyl propiolate, ethyl propiolate, 2-butynoic acid, ethyl 2-butynoate,4-pentynoic acid, 5-hexynonitrile, 2-octynoic acid,methyl 2-octynoate,methyl 2-nonynoate, acetylenedicarboxylic acid, diethylacetylenedicarboxylate, and dimethyl acetylenedicarboxylate.

[0032] Preferred alkynes are the 1-alkynes, propargyl alcohol,butynediol, propiolic acid and derivatives of acetylenedicarboxylicacid.

[0033] Particular preference is given to the use of ethyne(acetylene).

[0034] The reaction preferably takes place at a temperature of from 40to 200 °C.

[0035] The reaction particularly preferably takes place at a temperatureof from 70 to 130° C.

[0036] The reaction preferably takes place without a solvent in theH₃PO₃ melt.

[0037] The reaction preferably takes place in the presence of a solvent.

[0038] The solvent in which the reaction takes place is preferablyacetic acid or water.

[0039] The reaction preferably takes place by introducing gaseous ethyne(acetylene) at atmospheric pressure.

[0040] The reaction preferably takes place at superatmospheric pressure.

[0041] The manner of conducting the process is preferably such thatafter partial conversion the precipitating ethylenediphosphonic acid isfiltered off, and further ethyne(acetylene) is added after replacing thephosphorous acid consumed.

[0042] The present invention in particular also provides a process inwhich phosphorous acid is reacted with ethyne(acetylene) in the presenceof a cationic or noncationic free-radical initiator, or in the presenceof a peroxidic free-radical initiator, to give ethylenediphosphonicacid.

[0043] The present invention in particular also encompasses a process inwhich phosphorous acid is reacted with ethyne(acetylene) in the presenceof a cationic or noncationic free-radical initiator, or in the presenceof a peroxidic free-radical initiator, to give ethylenediphosphonicacid, and this is removed continuously from the reaction mixture by acirculating filter system, and the phosphorous acid consumed is likewisereplaced continuously by fresh acid.

[0044] The desired ethylenediphosphonic acids are obtained with highselectivity and high purity.

[0045] Either the phosphorous acid or else the alkynes may be used inexcess, since the reaction partners always react in a molar ratio of 2to 1 (phosphorous acid to alkyne).

EXAMPLES

[0046] The examples below illustrate the invention:

Example 1 Ethylenediphosphonic Acid

[0047] Gaseous ethyne(acetylene) was passed for a period of 10 h at atemperature of about 100° C. into 164 g (2 mol) of molten phosphorousacid in a heatable glass tubular reactor with gas-feed frit. At the sametime, a solution of 23 g (0.1 mol) of ammonium peroxodisulfate in 50 gof water was metered in uniformly over the same period. After acontinued reaction time of 0.5 h, removal of the ethyne(acetylene) bypassing nitrogen through the mixture, and cooling to room temperature,the reaction mixture was freed from the water which had been introduced,filtered, washed twice, on each occasion using 200 ml of water, anddried at 130° C. under the suction provided by a water jet. This gave 82g of a white crystalline solid with a melting point of 211° C.,corresponding to a yield of 77.4%, based on the phosphorous acid used.Elemental analysis confirms the proposed structure: P: calc. 33.7%/found31.6%; C.: calc. 26.1%/found 26.7%; H: calc. 5.4%/found 5.7%; ³¹P NMRspectrum (NaOD): δ=30 ppm (singlet); Purity (³¹P NMR): 99%.

Example 2: Ethylenediphosphonic Acid

[0048] Gaseous ethyne(acetylene) was passed for a period of 10 h at atemperature of about 100° C. into 164 g (2 mol) of molten phosphorousacid in a heatable glass tubular reactor with gas-feed frit. At the sametime, a solution of 23 g (0.1 mol) of ammonium peroxodisulfate in 50 gof water, and also 107 g of molten phosphorous acid, were metered inuniformly over the same period. During the reaction, the reactionmixture was continuously freed from precipitating ethylenediphosphonicacid by way of a frit and equipment for pumped circulation. The filtercake was washed twice, on each occasion with 200 ml of water, and driedat 130° C. under the suction provided by a water jet. This gave 69 g ofethylenediphosphonic acid at 99% purity (³¹P NMR), corresponding to ayield of 65%, based on the amount of phosphorous acid starting materialused. Ethyne(acetylene) was then passed into the reaction mixture underthe same conditions, whereupon more ethylenediphosphonic acidprecipitated.

1. A process for preparing ethylenediphosphonic acids of the formula I

where R₁ and R₂ may be identical or different and are hydrogen, acarboxy group, a carboxylic acid derivative, an unsubstituted orsubstituted alkyl group having from 1 to 10 carbon atoms, phenyl,benzyl, or alkyl-substituted aromatic systems, which comprises reactingphosphorous acid (H₃PO₃) directly with alkynes.
 2. The process asclaimed in claim 1, wherein the phosphorous acid is reacted with alkynesin the presence of a free-radical initiator.
 3. The process as claimedin claim 1, wherein the free-radical initiator used comprises azocompounds.
 4. The process as claimed in claim 1, wherein the azocompounds comprise cationic and/or noncationic azo compounds.
 5. Theprocess as claimed in claim 1, wherein the cationic azo compounds usedcomprise 2,2′-azobis(2-amidinopropane)dihydrochloride or2,2′-azobis(N,N′-dimethyleneisobutyramidine)dihydrochloride.
 6. Theprocess as claimed in claim 1, wherein the non-cationic azo compoundsused comprise azobis(isobutyronitrile), 4,4′-azobis(4-cyanopentanoicacid), and/or 2,2′-azobis(2-methylbutyronitrile).
 7. The process asclaimed in claim 1, wherein the free-radical initiators used compriseperoxidic inorganic and/or peroxidic organic free-radical initiators. 8.The process as claimed in claim 7, wherein the peroxidic inorganicfree-radical initiators used comprise hydrogen peroxide, ammoniumperoxodisulfate, and/or potassium peroxodisulfate.
 9. The process asclaimed in claim 7, wherein the peroxidic organic free-radicalinitiators used comprise dibenzoyl peroxide, di-tert-butyl peroxide,and/or peracetic acid.
 10. The process as claimed in claim 1, whereinthe free-radical initiators are metered in continuously during thereaction.
 11. The process as claimed in claim 1, wherein thefree-radical initiators metered in continuously during the reaction arein the form of a solution in the alkyne.
 12. The process as claimed inclaim 1, wherein the free-radical initiators metered in continuouslyduring the reaction are in the form of a solution in the solvent used.13. The process as claimed in claim 1, wherein the alkynes have theformula II R₁—C≡C—R₂  (II) where R₁ and R₂ are identical or differentand are hydrogen, a carboxy group, a carboxylic acid derivative, anunsubstituted or substituted alkyl group having from 1 to 10 carbonatoms, phenyl, benzyl, or alkyl-substituted aromatic systems.
 14. Theprocess as claimed in claim 1, wherein the alkynes are ethyne(acetylene), phenylacetylene, diphenylacetylene, propyne, 1-butyne,2-butyne, 1-phenylbutyne, 1-pentyne, 2-pentyne, 1-phenyl-1-pentyne,1-hexyne, 2-hexyne, 3-hexyne, 1-phenyl-1-hexyne, 1-heptyne, 1-octyne,4-octyne, 1-nonyne, 1-decyne, 1-dodecyne, the alkynols propargylalcohol, 1-butyn-3-ol, 2-butyn-1-ol, 2-butyne-1,4-diol, 1-pentyn-3-ol,2-pentyn-1-ol, 4-pentyn-1-ol, 1-octyn-3-ol, 3-nonyn-1-ol, 3-decyn-1-ol,and also propargyl chloride, propargyl bromide, propargylamine,propiolic acid, methyl propiolate, ethyl propiolate, 2-butynoic acid,ethyl 2-butynoate, 4-pentynoic acid, 5-hexynonitrile, 2-octynoic acid,methyl 2-octynoate, methyl 2-nonynoate, acetylenedicarboxylic acid,diethyl acetylenedicarboxylate, and dimethyl acetylenedicarboxylate. 15.The process as claimed in claim 1, wherein the alkynes used are1-alkynes, propargyl alcohol, butynediol, propiolic acid, or derivativesof acetylenedicarboxylic acid.
 16. The process as claimed in claim 1,wherein the alkyne used comprises ethyne(acetylene).
 17. The process asclaimed in claim 1, wherein the reaction takes place at a temperature offrom 40 to 200° C.
 18. The process as claimed in claim 1, wherein thereaction takes place at a temperature of from 70 to 130° C.
 19. Theprocess as claimed in claim 1, wherein the reaction takes place withoutsolvent in the H₃PO₃ melt.
 20. The process as claimed in claim 1,wherein the reaction takes place in the presence of a solvent.
 21. Theprocess as claimed in claim 20, wherein the solvent is acetic acid orwater.
 22. The process as claimed in claim 1, wherein the reaction takesplace by introducing gaseous ethyne(acetylene) at atmospheric pressure.23. The process as claimed in claim 1, wherein the reaction takes placeat superatmospheric pressure.
 24. The process as claimed in claim 1,wherein phosphorous acid is reacted with ethyne(acetylene) in thepresence of a cationic or noncationic free-radical initiator, or in thepresence of a peroxidic free-radical initiator, to giveethylenediphosphonic acid.
 25. The process as claimed in claim 1,wherein phosphorous acid is reacted with ethyne(acetylene) in thepresence of a cationic or noncationic free-radical initiator, or in thepresence of a peroxidic free-radical initiator, to giveethylenediphosphonic acid, and this is removed continuously from thereaction mixture by a circulating filter system, and the phosphorousacid consumed is likewise replaced continuously by fresh acid.